In general, a solar cell has electrodes respectively on the front and rear side of a semiconductor substrate, and as a front electrode is disposed on the front side, which is a light-receiving side, a light-receiving area decreases by the area of the front electrode. To overcome the problem of reducing the light-receiving area, a back-contact type of solar cell has been proposed.
A back-contact type of solar cell is divided into MWA (metallization wrap around), MWT (metallization wrap-through), EWT (emitter wrap-through), back-junction, and the like according to the structure.
FIG. 1 shows an enlarged part of the rear side (i.e., a side opposite to the front side facing the sun during normal operation) of a common emitter wrap-through solar cell (hereinafter referred to as ‘EWT solar cell’). According to FIG. 1, both a base electrode (15) and an emitter electrode (25) having different conductivity are located on the rear side of the EWT solar cell, and the emitter electrode (25) is formed in a trench that is formed on the rear side of the substrate for the separation of p-n junction. That is, a common EWT solar cell has a structure with a height difference between the base electrode (15) and the emitter electrode (25) (for example, a structure wherein the base electrode is about 10 to 30 μm higher than the emitter electrode).
Meanwhile, an energy conversion efficiency measurement error of the EWT solar cell may be minimized as uniform pressure is applied to the rear side of the cell, but due to the structural property of the EWT solar cell (particularly, a height difference between the base electrode and the emitter electrode), non-uniform contact pressure is generated and thus a large energy conversion efficiency measurement error is generated.
In the preparation process of a common EWT solar cell, a base electrode and an emitter electrode are formed by printing or coating each electrode forming material on corresponding area of a substrate, but in the printing or coating process, there is a limitation in exact confirmation of the alignment state, That is confirming if each electrode is formed on the exact desired location.
Further, due to the structural property of the EWT solar cell, despite the separation of the p-n junction, since the distance between the base electrode and the emitter electrode is small, a leakage current may be generated.